Liquid pump and sealing mechanism

ABSTRACT

The present invention relates to a liquid pump having improved characteristics concerning a sealing mechanism utilizing magnets. A liquid pump comprises: a sealing mechanism employing a method whereby a space between a motor casing for storing an electric motor and a pump casing in which an impeller fixed to the tip of a rotating shaft of the electric motor is disposed and a pump chamber is formed is enclosed in a watertight manner by a cylindrical frame, and a pair of sealing members composed of a rotating sealing member and a stationary sealing member are disposed around the rotating shaft of the electric motor, and opening and closing of the seal by joining and separation of both sealing members is controlled by magnetic force of magnets to be displaced by a rotation of the motor rotating shaft, and is characterized: in that (1) the sealing members are composed of an annular rotating seal attached to the lower surface of a rotary base member fixed to the motor rotating shaft and a flexible stationary seal which is joined and separated with respect to the rotating seal,(2) in the rotary base member on which the rotating seal is disposed, disposed are movable magnets to be displaced by centrifugal force due to a rotation of the rotary base member, and on the other hand, on the upper-surface side of a vertical sliding member to which the flexible stationary seal is fixed, disposed is a stationary magnet. Moreover, the flexible stationary seal utilized in the above-described liquid pump is characterized in that the whole body is cylindrical, at the upper and lower end portions and the side surface portion, connecting portions to the stationary and movable members are formed, and at the middle portion, an elastic portion is formed.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a liquid pump using an electric motor as a driving source, and more particularly, it relates to a liquid pump having improved characteristics in a sealing mechanism utilizing magnets.

[0003] 2. Description of the Prior Art

[0004] In a liquid pump, in order to prevent a liquid from intruding into a motor casing from the side of a pump casing through a rotating shaft, a bearing portion of the rotating shaft is provided with a sealing mechanism of a construction for disposing a mechanical seal or of a construction for disposing a packing.

[0005] In a mechanism for sealing at the circumference of the rotating shaft, the sealing members are always in contact with the rotating shaft irrespective of the operating state or non-operating state of an electric motor and, therefore, easily wear down and impose a heavy maintenance burden.

[0006] In addition, in the liquid pump, depending on the usage place and application, not only the liquid but also minute solid content intrude into the circumference of the rotating shaft, and consequently, in the prior mechanism for sealing at the circumference of the rotating shaft, a problem such that the sealing members are easily damaged also exists.

[0007] In view of the above circumstances, sealing mechanism utilizing electromagnets have been proposed and carried out. For example, Japanese Patent Publication No. H01-43159 teaches a construction, wherein a ring seal fixed in a brim shape to a rotating shaft and a ring seal to be attached to a cylindrical supporting body disposed in a manner shift-able in the axial direction of the rotating shaft are prepared, both are opposed to each other, and the cylindrical supporting body is operated by an electromagnet, and when an electric motor is in operation, by turning on the effect of the electromagnet, the cylindrical supporting body is shifted to closely fit both ring seals to create a sealing state, and when an electric motor is not in operation, by turning off the effect of the electromagnet, the cylindrical supporting body is restored by a spring or the like to release close fitting between both ring seals.

[0008] On the other hand, Japanese Patent Publication No. S62-46717 and Japanese Patent Publication No. S62-49477 teach a construction, wherein joining and separation of opposed ring seals are controlled by centrifugal force produced by a rotation of a rotating shaft when an electric motor is in operation.

[0009] In addition to the above, a construction for sealing by utilizing centrifugal force produced by a rotation of a rotating shaft is disclosed in Japanese Unexamined Patent Publication No. H07-280105, etc., however, this is carried out by only mechanical structures and is therein different from the construction of the present invention.

[0010] Since the sealing mechanism taught in the above-described Japanese Patent Publication No. H01-43159 has a construction wherein joining and separation of the opposed ring seals are carried out by turning on and off of the electromagnet, technical problems remain, such that (1) a power supply circuit for operating the electromagnet is required, which results in a high cost, moreover, (2) since power supply voltages are not uniform among countries and regions, an adjustment is required prior to utilization, (3) the space where the electromagnet is arranged requires water-tightness, which complicates the mechanism, (4) since temperature of the watertight space rises due to heat generated by the electromagnet and condensation easily condenses in a stop state, there is a concern for malfunction.

[0011] On the other hand, Japanese Patent Publications No. S62-46717 and No. S62-49477 concern, as described above, a sealing mechanism in that joining and separation of the opposed ring seals are controlled by centrifugal force produced by a rotation of the rotating shaft when an electric motor is in operation, however, since all components are mechanically structured, technical problems remain, such that (1) accurate processing and assembling of members or operating adjustments are required, and moreover, (2) a malfunction easily occurs when minute solid components, etc., intrude, and the maintenance burden is great.

[0012] In particular, in a prior sealing mechanism, an O-ring or an oil seal is required in a sliding portion for driving a sealing member up and down, however, in some cases, expansion, corrosion and the like due to chemicals exist in the sliding portion and the sealing member cannot smoothly follow the movement of the rotating shaft due to frictional resistance. Consequently, the prior liquid pump has a problem of an increased maintenance burden

SUMMARY OF THE INVENTION

[0013] The present invention has been made with the objective of solving the problems of the prior arts concerning liquid pumps, and discloses a liquid pump having a sealing mechanism constructed so that (1) in order to prevent the sealing members from wearing down, control can be performed so as to release the sealing when the rotating shaft is rotating, (2) no power source is required for seal control, (3) watertight-ness of a seal control portion can be easily maintained, (4) maintenance burden is relieved, and (5) the number of components is small, the mechanism is simple, and manufacturing costs can be reduced.

[0014] A liquid pump and a sealing mechanism according to the present invention are characterized in the following constructions.

[0015] 1. A liquid pump comprising: a sealing mechanism employing a method whereby a space between a motor casing for an electric motor and a pump casing in which an impeller fixed to the tip of a rotating shaft of said electric motor is disposed and a pump chamber is formed is enclosed in a watertight manner by a cylindrical frame, and a pair of sealing members composed of a rotating sealing member and a stationary sealing member are disposed around the rotating shaft of said electric motor, and opening and closing of the seal by joining and separation of both sealing members is controlled by magnetic force of magnets to be displaced by a rotation of the motor rotating shaft, wherein said sealing mechanism is constructed such that

[0016] (1) the sealing members are composed of an annular rotating seal attached to the lower surface of a rotary base member fixed to the motor rotating shaft and a flexible stationary seal which is joined and separated with respect to said rotating seal,

[0017] (2) movable magnets to be displaced by centrifugal force due to a rotation of the rotary base member are disposed in the rotary base member assembled said rotating seal, and on the other hand, stationary magnets are disposed on the upper-surface side of a vertical sliding member to which said flexible stationary seal is fixed, and

[0018] (2-1) when the motor rotating shaft is stopped, by the N-poles or S-poles of the movable magnets at their original positions, an opposite pole (the S-pole or N-pole) of the stationary magnet is attracted and said vertical sliding member is drawn upward, and consequently, the upper surface of the flexible stationary seal is joined to (brought into contact with) the lower surface of the rotating seal to seal an air chamber, and

[0019] (2-2) when the motor rotating shaft is rotating at an appointed number of rotations, the sealing members are controlled so that the same poles of the movable magnets displaced from their original positions by centrifugal force and the stationary magnet repel each other and the vertical sliding member is depressed downward, and consequently, the upper surface of the flexible stationary seal is separated from the lower surface of the rotating seal to release the seal of the air chamber.

[0020] 2. A liquid pump comprising: a sealing mechanism employing a method whereby a space between a motor casing for an electric motor and a pump casing in which an impeller fixed to the tip of a rotating shaft of said electric motor is disposed and a pump chamber is formed is enclosed in a watertight manner by a cylindrical frame, and a pair of sealing members composed of a rotating sealing member and a stationary sealing member are disposed around the rotating shaft of said electric motor, and opening and closing of the seal by joining and separation of both sealing members is controlled by magnetic force of magnets to be displaced by a rotation of the motor rotating shaft, wherein said sealing mechanism is constructed such that

[0021] (1) the sealing members are composed of an annular rotating seal attached to the lower surface of a rotary base member fixed to the motor rotating shaft and a flexible stationary seal which has, at its upper end, an upper-surface portion that comes into contact with the lower surface of said rotating seal, and, at its middle portion, an elastic portion are formed, and, on its side surface, a cylindrical vertical sliding member, and whose lower end is fixed to a disk-like substrate fixed continuously to a pump casing,

[0022] (2) movable magnets to be displaced by centrifugal force due to a rotation of the rotary base member are disposed in the rotary base member assembled said rotating seal, and on the other hand, stationary magnets are disposed on the upper-surface side of a vertical sliding member to which said flexible stationary seal is fixed, and

[0023] (2-1) when the motor rotating shaft is stopped, by the N-poles or S-poles of the movable magnets at their original positions, an opposite pole (the S-pole or N-pole) of the stationary magnet is attracted and said vertical sliding member is drawn upward, and consequently, the upper surface of the flexible stationary seal is joined to (brought into contact with) the lower surface of the rotating seal to seal an air chamber, and

[0024] (2-2) when the motor rotating shaft is rotating at an appointed number of rotations, the sealing members are controlled so that the same poles of the movable magnets displaced from their original positions by centrifugal force and the stationary magnet repel each other and the vertical sliding member is depressed downward, and consequently, the upper surface of the flexible stationary seal is separated from the lower surface of the rotating seal to release the seal of the air chamber.

[0025] 3. A liquid pump comprising the sealing mechanism as set forth in the above 1 or 2, wherein a return of the movable magnets to their original positions is carried out by a repulsive force between the same poles and an attractive force to the opposite pole with respect to the stationary magnet.

[0026] 4. A sealing member utilized in the liquid pump as set forth in the above 1-3, wherein the whole body of said sealing member is formed as cylindrical, connecting portions to the stationary and movable members are formed at the upper and lower end portions and the side surface portion, and an elastic portion is formed at the middle portion.

[0027] 5. The sealing member as set forth in the above 4, which is formed of a material having flexibility.

[0028] 6. The sealing members as set forth in the above 4, wherein only the elastic portion is formed of a material having flexibility.

[0029] 7. The sealing member as set forth in any of the above 4-6, wherein the elastic portion is formed in an outwardly curved shape.

[0030] 8. The sealing members as set forth in any of the above 4-6, wherein the elastic portion is formed in an inwardly curved shape.

[0031] 9. The liquid pump as set forth in the above 1-3, wherein an annular sealing member is disposed between the upper-end margin of a fixing member for the stationary magnet and the end portion of a cylindrical attachment member disposed outside the rotary base member.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is a longitudinal sectional view of a main part showing an embodiment of the present invention.

[0033]FIG. 2 is a schematic plan view showing an arrangement example of the movable magnet.

[0034]FIG. 3 is a schematic plan view showing another arrangement example of the movable magnet.

[0035]FIG. 4 is an operation explanatory view of the sealing mechanism.

[0036]FIG. 5 is a sectional view of a main part showing the structure of contact surfaces of the rotational seal and flexible stationary seal.

[0037]FIG. 6 is a longitudinal sectional view of a main part showing two other embodiments according to the present invention.

[0038]FIG. 7 is an enlarged view of a main part showing another embodiment according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0039] Now, a liquid pump according to the present invention will be described in detail according to the attached drawings.

[0040] In FIG. 1, a motor case 10, in which an electric motor for driving a pump is disposed in a watertight condition, is, at its bottom portion, coupled to a cylindrical frame 12 for a pump by a flange 11. To the lower end of the cylindrical frame 12 for a pump, a pump casing 13 is attached in a fixed condition.

[0041] A rotating shaft 20 of the electric motor assembled in the motor case 10 in an airtight condition is extended below the flange 11, and to its tip, which reaches a pump chamber 14, an impeller 30 is attached.

[0042] At a lower-end side of the impeller 30, main vanes 31 are attached, and at an upper-end side, back vanes 32 are attached. Moreover, on the impeller 30, a brim shaped back-flow prevention seal 33 is disposed, and said back-flow prevention seal 33 has a function to prevent, in coordination with an opening portion of a partition plate 55, a liquid from suddenly intruding from the pump chamber 14 side when the rotating shaft 20 is stopped.

[0043] When the impeller 30 is rotated by driving of the electric motor, suction is produced by effects of the main vanes 31 and back vanes 32 disposed therein, and the liquid is suctioned from the direction of arrow A into a pump chamber 14 and is discharged in the direction of arrow B.

[0044] The above-described construction is basically identical to the construction of a conventional, well-known liquid pumps, and is not a characteristic construction of the present invention.

[0045] Now, a sealing mechanism which is characteristic of the present invention will be described.

[0046] At a position above the pump chamber 14 and in the interior enclosed by the cylindrical frame 12, a sealing mechanism (which will be described below) is assembled.

[0047] A central opening is fixed to the rotating shaft 20, and to the lower surface of a rotary base member 40 which rotates in accordance with the rotation of the rotating axis 20, a rotating seal 41 is attached. Although the basic shape of the rotating seal 41 is a ring shape, the shape of its section is not necessarily rectangular as shown in FIG. 1. Nevertheless, since the rotating seal 41 is designed to perform sealing, it is necessary that at least the lower-side surface thereof has a part to closely fit to the upper surface of a flexible stationary seal 50 (which will be described later).

[0048] As a material to form the rotating seal 41, various materials generally used as sealing members, such as natural or synthetic rubber and synthetic resin, can be used, and in general, a material having resistance to oil and other chemical agents, etc., is preferable, although this depends on the application field of the liquid pump.

[0049] The flexible stationary seal 50 is disposed opposite to the aforementioned rotating seal 41. “Flexible” for the flexible stationary seal 50 means that, in FIG. 1, the whole or a part thereof is flexible in the up-and-down direction, and “stationary” means that the seal is independent of the rotating shaft 20 and does not rotate. It is satisfactory that the flexible stationary seal 50 used in the present invention is constructed so as to join and separate with respect to the rotating seal 41.

[0050] A protrusion formed on the side surface of the flexible stationary seal 50 of the present embodiment is attached to the inner wall of a disk-like vertical sliding member 51 by utilizing elasticity, while the lower-end portion of the flexible stationary seal 50 is fixed to a disk-like fixing member 52. The fixing member 52 to fix the lower end of the flexible stationary seal 50 is attached on a disk-like substrate 54, and furthermore, the substrate 54 is fixed on the upper surface of the disk-like partition plate 55 for partition between the pump chamber 14 and an air chamber 15. Accordingly, the respective members in a fixed condition with respect to the flexible stationary seal 50 are free from rotation of the rotating shaft 20 and do not rotate.

[0051] The vertical sliding member 51 is restricted by turn prevention bolts 53 and, consequently, does not turn, and can shift in only the up-and-down direction by sliding along the turn prevention bolts 53.

[0052] The above construction is characterized in that it is unnecessary to slide the fixing member 52 and disk-like substrate 54 that support the flexible stationary seal 50 along the inner surface of the cylindrical frame 12 and in that the vertical sliding member 51 that is continuously provided from the flexible stationary seal 50 has, at a sliding surface with respect to other members including the inner surface of the cylindrical frame 12, no sealing mechanism such as an O-ring or a mechanical seal or the like as is found in a sealing mechanism of a prior liquid pump.

[0053] The flexible stationary seal 50 has an elastic portion 57 whose section is U-shaped and has, consequently, elasticity in the up-and-down direction. The elastic portion 57 can be constructed in various shapes such as a bellows shape in which a plurality of U-shaped portions are continued, and accordingly, the sectional shape of the flexible stationary seal 50 including the elastic portion 57 is not limited to that as shown in FIG. 1.

[0054] The flexible stationary seal 50 may be formed of a material having flexibility such as natural or synthetic rubber or synthetic resin, or it may employ a combined structure in which only the part of the elastic portion 57 is formed of a flexible member. Accordingly, for example, the elastic portion 57 may be formed of a stainless steal bellows. Furthermore, similar to the above-described rotating seal 41, it is generally preferable that the flexible stationary seal 50 is formed of a material having resistance to oil and other chemical agents, etc., and it is also preferable to enhance the chemical resistance by processing the front surface by a fluorocarbon resin treatment.

[0055] Now, a description will be given of a joining (contact) structure between the lower surface of the rotating seal 41 and the upper surface of the flexible stationary seal 50. Hereinafter, the term “contact” will be used for “joining.”

[0056] Since these surfaces have a structure in which when the lower surface of the rotating seal 41 and the upper surface of the flexible stationary seal 50 are in contact, the seal is in an ON state, and when both are separated, the seal turns OFF, the contact surfaces of both may be basically flat and smooth. Nevertheless, when a condition where the rotating shaft 20 is rotating at an appointed number of rotations, a condition where the same is rotating below the appointed number of rotations, and a condition where the same is stopped are compared, there is a difference in pressure of the air chamber 15 (the space from the back-flow prevent seal 33 to the rotary base member 40 and rotating seal 41), and the inner pressure of the air chamber 15 becomes maximum When the rotating shaft 20 is stopped. Accordingly, it is preferable to construct the contact surfaces of both so that the contact state between the lower surface of the rotating seal 41 and the upper surface of the flexible stationary seal 50 becomes strongest when the inner pressure of the air chamber is maximized.

[0057] A construction to satisfy the above will be described in detail. First, in the construction as shown in FIG. 5, the upper surface of the flexible stationary seal 50 is formed with two stages having a shape wherein an upper-surface inner-peripheral side 50A is inclined toward the outer periphery, an upper-surface outer-peripheral side 50B is approximately horizontally formed, and the tip of the upper-surface inner-peripheral side 50A is protruded from the surface of the upper-surface outer-peripheral side 50B. Accordingly, from the state where the rotating seal 41 and the flexible stationary seal 50 are separated, as driving of the pump is stopped and the number of rotations of the rotating axis 20 is decreased, the flexible stationary seal 50 rises due to the effects of magnets 43 ad 56. Consequently, when, first, the forefront tip portion of the upper-surface inner-peripheral side 50A comes in contact with the lower surface of the rotating seal 41 and then the flexible stationary seal 50 is further attracted upward by the force of the magnets 43 and 56, the forefront tip portion of the upper-surface inner-peripheral side 50A is deformed and the surface of the upper-surface outer-peripheral side 50B comes in contact with the lower surface of the rotating seal 41.

[0058] Although the above construction employs a mode where the upper surface of the flexible stationary seal 50 is formed with two stages, any construction may be employed as long as close fitting is possible, such as a mode where the whole upper surface is formed in an inclined manner descending toward the outside (an umbrella shape).

[0059] Since the upper surface of the flexible stationary seal 50 has the above construction, even when the lower surface of the rotating seal 41 has a plane shape, a strong contact pressure can be obtained compared to a construction wherein the whole upper surface of the flexible stationary seal 50 is a plane, thus the sealing effect is high.

[0060] In the rotary base member 40 to which the rotating seal 41 is attached, magnet housing 42 are prepared and therein the movable magnets 43 are disposed, and in the vertical sliding member 51 disposed on the side surface of the flexible stationary seal 50, the stationary magnet 56 is disposed in a magnet housing.

[0061] As shown in FIG. 2, the movable magnets 43 are assembled in the magnet housings 42 prepared in radial direction in the rotary base member 40 and laid out so that the respective N-poles are located on the center side. Although the movable magnets 43 are arranged at four locations in the illustrated mode, the quantity is not limited. As the movable magnet 43 disposed in each magnet housing 42, a stick-shaped single magnet is basically employed, however, the shape and quantity are not limited hereto and, for example, the mode may be such that two rectangular magnets are disposed so as to have mutually opposite polarities.

[0062] As shown in FIG. 2, the section of the stationary magnet 56 disposed in the vertical sliding member 51 has an annular shape, is arranged so that its N-pole is located upward, and corresponds to the movable magnets 43 disposed in radial direction. Herein, the movable magnets 43 and the stationary magnet 56 may be disposed so that the respective polarities become opposite to those shown in FIG. 2.

[0063] In the mode shown in FIG. 2, the magnet housing 42 for the movable magnets 43 are linearly disposed in the direction of circumference, whereas the present invention includes, as shown in FIG. 3, a mode wherein the magnet housing 42 are prepared in a manner inclining in the opposite directions to the directions shown by the arrows.

[0064] As shown in FIG. 2 and FIG. 3, when the rotating shaft 20 is stopped (including the condition where the number of revolutions is below an appointed number of rotations), that is, when the movable magnets 43 and the stationary magnet 56 are in the positional condition as shown in FIG. 1, the S-poles of the movable magnets 43 and the N-pole of the stationary magnet 56 attract each other, and consequently, the vertical sliding member 51 is attracted in the upper direction in FIG. 1, the upper surface of the flexible stationary seal 50 is brought into contact with the lower surface of the rotating seal 41, and the sealing function turns ON.

[0065] Next, when the rotating axis 20 is rotating at an appointed number of rotations, the rotary base member 40 is also simultaneously rotated, therefore, the movable magnets 43 are blown in the direction of circumference by centrifugal force, and their N-poles are located on the upper surface of the N-pole of the stationary magnet 56 prepared in the vertical sliding magnet 51 (see the rotating conditions of FIG. 2 and FIG. 3). In this condition, the N-poles of the movable magnets 43 and the N-pole of the stationary magnet 56 repel each other and, consequently, the vertical sliding member 51 is depressed in the lower direction as shown in FIG. 4. As a result, contact of the upper surface of the flexible stationary seal 50 with the lower surface of the rotating seal 41 is released, and the sealing function turns OFF.

[0066] In the above construction, it is necessary to give a description of a mechanism whereby the movable magnets 43, which were blown in the direction of circumference by centrifugal force when the rotating shaft 20 was rotating at the appointed number of rotations, are returned to the original positions as shown in FIG. 1 when the rotating shaft 20 stops (including when the rotating shaft 20 is rotating at a number of rotations less than the appointed number of rotations).

[0067] As a first mode to enable the above-described mechanism, a construction can be mentioned, wherein at a point in time where rotation of the rotating shaft 20 is stopped and the centrifugal force which was blowing out the movable magnets 43 in the direction of circumference is weakened, an attracting force whereby the S-poles of the movable magnets 43 and the N-pole of the magnet 56 attract each other becomes great, and the movable magnets 43 automatically return to the original positions.

[0068] As a second mode, a construction can be mentioned, wherein, as shown by the virtual lines in FIG. 1, the movable magnets 43 automatically return to the original positions by utilizing repulsion of an elastic member 44 such as a helical spring or rubber. It may be a construction, wherein the repulsion of this elastic member 44 and the repulsive and attractive magnetic forces of the magnets 43 and 56 are utilized together.

[0069] As a third mode, a construction can be mentioned, wherein the movable magnets 43 are returned by their own gravity when the magnet housing 42 for storing the movable magnets 43 are disposed in a manner inclining in the center direction and no load of centrifugal force exists. This mode is effective only when a liquid pump is utilized while a vertical condition is maintained at all times.

[0070] When the flexible stationary seal 50 is utilized in combination with the rotating seal 41, effects as described above are provided, and the “sealing member characterized in that the whole body is cylindrical, at the upper and lower end portions and the side surface portion, connecting portions to the stationary and movable members are formed, and at the middle portion, an elastic portion is formed” according to the present invention can be utilized as a flexible sealing member to divide an inner space of a cylindrical object into two in the longitudinal direction for a pump such as a liquid pump and other flexible seal purposes in various fields.

[0071] Now, a fourth mode of the present invention will be described according to FIG. 6. In the drawing, for the sake of ease in realizing the contents of the invention, two different modes are separately expressed on the left and right sides across the centerline shown by symbols C-C. The basic component members are the same as those of the embodiment as shown in FIG. 1 and these are shown by identical symbols.

[0072] The mode expressed in the left half is more advanced, and has the following advantages compared with the mode expressed in the right half. The first advantage is in a construction of the elastic portion 57A provided for the flexible stationary seal 50. The elastic portion 57B expressed in the right half is formed in an inwardly bending shape, whereas the elastic portion 57A expressed in the left half is formed in an outwardly bending (swelling) shape. The difference in the shapes between the two displays a difference in capacities to absorb the pressure of the pump chamber side. As mentioned above, when the number of rotations of the motor rotating shaft 20 is gradually decreased and the motor rotating shaft 20 reaches a stopped condition, the inner pressure of the air chamber 15 (as shown in FIG. 1, the inner space from the back-flow prevent seal 33 to the rotary base member 40 and rotating seal 41) is maximized. And at this time, the pressure of the air chamber 15 directly effects the sealing structure which functions at the contact surfaces between the lower surface of the rotating seal 41 and the upper surface of the flexible stationary seal 50, and if the pressure of the air chamber 15 is excessively heightened, the sealing structure may finally be broken.

[0073] As described above, even if the pressure of the air chamber 15 is excessively heightened, since the elastic portion 57A has an outwardly swelling structure in the mode expressed in the left half of FIG. 6, the excessively high pressure of the air chamber 15 effects the elastic portion 57A, functions as if to blow up a balloon, whereby the pressure is quickly absorbed. Accordingly, compared with the mode expressed in the right half of FIG. 6, in which a high pressure directly effects at the sealing structure that functions at the contact surfaces between the lower surface of the rotating seal 41 and the upper surface of the flexible stationary seal 50, the seal easily turns OFF even with a weak repulsive magnetic force when the rotating seal 41 rotates at restarting.

[0074] In the mode shown in the right half of FIG. 6, since the elastic portion 57A is curved inward, its capacity to absorb an inner pressure rapidly increased at stopping is weak and, on the other hand, a high pressure is exerted to the sealing structure that functions at the contact surfaces between the lower surface of the rotating seal 41 and the upper surface of the flexible stationary seal 50, and as a result, sealing ability is improved. Nevertheless, this aspect also results in that if the repulsive force between the movable magnets 43 and stationary magnet 56 is weak at restarting, the contact surfaces between the lower surface of the rotating seal 41 and the upper surface of the flexible stationary seal 50 are not easily separated and the sealing condition remains ON, and a burden is exerted on rotation of the rotating shaft 20.

[0075] Next, capacity of the space formed around the contact surfaces between the lower surface of the rotating seal 41 and the upper surface of the flexible stationary seal 50, or the positional relationship between the movable magnet 43 and stationary magnet 56 comes into question.

[0076] In the mode expressed in the right half of FIG. 6, with respect to the rotary base member 40 on which the movable magnets 43 are disposed, a vertical sliding portion 51 which is structured to move in the up-and-down direction with long strokes and has a stationary magnet 56 on its upper-end side is disposed, and a space with a large capacity is formed outside the sealing structure that functions at the contact surfaces between the lower surface of the rotating seal 41 and the upper surface of the flexible stationary seal 50. In contrast thereto, in the mode expressed in the left half of FIG. 6, the movable magnets 43 and the stationary magnet 56 are disposed close to the sealing structure, and capacity of the space formed outside the sealing structure is small. Accordingly, even if liquid leakage occurs outside the sealing structure, in the mode expressed in the left half of FIG. 6, the quantity of liquid leakage can be limited to as little as possible.

[0077] The third characteristic point is already obvious from the above description. Namely, compared to that the vertical movement stroke of the vertical sliding member 51 to support the stationary magnet 56 is long in the mode expressed in the right half of FIG. 6, ON/OFF of the sealing structure is operated with very short vertical movement strokes in the mode expressed in the left half of FIG. 6. The difference between the two is a difference in responding quickness (strength) of the stationary magnet 56 which repulses the polarity of the movable magnets 43 and is, furthermore, displayed as ease in fine adjustment of the magnets, etc.

[0078] An embodiment shown in FIG. 7 will be described. This embodiment is characterized in a structure wherein an annular sealing member shown by a symbol 60 is arranged between the upper-end marginal portion of the fixing member 52 and a cylindrical attachment member 61 arranged outside the rotary base member 40. Namely, this annular seal 60 is made to respond to the movement of the sealing structure composed of the rotating seal 41 and flexible stationary seal 50 and is structured, as illustrated, so as to be separated in the arrow direction A-A when the rotating shaft 20 is rotating and the sealing structure is OFF, and so as to be operated in reverse to the arrow direction A-A and reach a compressed state when the rotation of the rotating shaft 20 is stopped and the sealing structure is ON, so that the flow channel shown by the arrows is closed.

[0079] The above structure is a safety mechanism which is caused to function as a reserve in a case where the sealing structure composed of the rotating seal 41 and the flexible stationary seal 50 did not function even when rotation of the rotating shaft 20 was stopped and is, therefore, not a necessary construction in all embodiments.

[0080] Since a liquid pump according to the present invention has the above-described construction, advantages are provided such that (1) the sealing members can be controlled so as to be separated when the rotating shaft is in operation and so as to function only when the rotating shaft is not in operation, therefore, the members are effectively prevented from wearing down compared with the prior construction in that the members are in operation at all times, (2) a constant voltage source is unnecessary for seal control, therefore, the liquid pump can be utilized in countries and regions where voltage are variable, (3) ON/OFF of the sealing members are carried out by only the action of magnets that are mechanically out of contact, and the magnet housing can easily maintain watertight-ness, (4) sealing of the part for driving the sealing members is unnecessary, contamination of the O-ring or mechanical seal part as in the prior sealing mechanism does not occur, and the maintenance burden is relieved, and (5) the number of components is small, the mechanism is simple, and manufacturing costs can be reduced. 

What is claimed is:
 1. A liquid pump comprising: a sealing mechanism employing a method whereby a space between a motor casing for an electric motor and a pump casing in which an impeller fixed to the tip of a rotating shaft of said electric motor is disposed and a pump chamber is formed is enclosed in a watertight manner by a cylindrical frame, and a pair of sealing members composed of a rotating sealing member and a stationary sealing member are disposed around the rotating shaft of said electric motor, and opening and closing of the seal by joining and separation of both sealing members is controlled by magnetic force of magnets to be displaced by a rotation of the motor rotating shaft, wherein said sealing mechanism is constructed such that (1) the sealing members are composed of an annular rotating seal attached to the lower surface of a rotary base member fixed to the motor rotating shaft and a flexible stationary seal which is joined and separated with respect to said rotating seal, (2) movable magnets to be displaced by centrifugal force due to a rotation of the rotary base member are disposed in the rotary base member assembled said rotating seal, and on the other hand, stationary magnets are disposed on the upper-surface side of a vertical sliding member to which said flexible stationary seal is fixed, and (2-1) when the motor rotating shaft is stopped, by the N-poles or S-poles of the movable magnets at their original positions, an opposite pole (the S-pole or N-pole) of the stationary magnet is attracted and said vertical sliding member is drawn upward, and consequently, the upper surface of the flexible stationary seal is joined to (brought into contact with) the lower surface of the rotating seal to seal an air chamber, and (2-2) when the motor rotating shaft is rotating at an appointed number of rotations, the sealing members are controlled so that the same poles of the movable magnets displaced from their original positions by centrifugal force and the stationary magnet repel each other and the vertical sliding member is depressed downward, and consequently, the upper surface of the flexible stationary seal is separated from the lower surface of the rotating seal to release the seal of the air chamber.
 2. A liquid pump comprising: a sealing mechanism employing a method whereby a space between a motor casing for an electric motor and a pump casing in which an impeller fixed to the tip of a rotating shaft of said electric motor is disposed and a pump chamber is formed is enclosed in a watertight manner by a cylindrical frame, and a pair of sealing members composed of a rotating sealing member and a stationary sealing member are disposed around the rotating shaft of said electric motor, and opening and closing of the seal by joining and separation of both sealing members is controlled by magnetic force of magnets to be displaced by a rotation of the motor rotating shaft, wherein said sealing mechanism is constructed such that (1) the sealing members are composed of an annular rotating seal attached to the lower surface of a rotary base member fixed to the motor rotating shaft and a flexible stationary seal which has, at its upper end, an upper-surface portion that comes into contact with the lower surface of said rotating seal, and, at its middle portion, an elastic portion are formed, and, on its side surface, a cylindrical vertical sliding member, and whose lower end is fixed to a disk-like substrate fixed continuously to a pump casing, (2) movable magnets to be displaced by centrifugal force due to a rotation of the rotary base member are disposed in the rotary base member assembled said rotating seal, and on the other hand, stationary magnets are disposed on the upper-surface side of a vertical sliding member to which said flexible stationary seal is fixed, and (2-1) when the motor rotating shaft is stopped, by the N-poles or S-poles of the movable magnets at their original positions, an opposite pole (the S-pole or N-pole) of the stationary magnet is attracted and said vertical sliding member is drawn upward, and consequently, the upper surface of the flexible stationary seal is joined to (brought into contact with) the lower surface of the rotating seal to seal an air chamber, and (2-2) when the motor rotating shaft is rotating at an appointed number of rotations, the sealing members are controlled so that the same poles of the movable magnets displaced from their original positions by centrifugal force and the stationary magnet repel each other and the vertical sliding member is depressed downward, and consequently, the upper surface of the flexible stationary seal is separated from the lower surface of the rotating seal to release the seal of the air chamber.
 3. A liquid pump comprising the sealing mechanism as set forth in claim 1 or 2, wherein a return of the movable magnets to their original positions is carried out by a repulsive force between the same poles and an attractive force to the opposite pole with respect to the stationary magnet.
 4. A sealing member utilized in the liquid pump as set forth in claims 1-3, wherein the whole body of said sealing member is formed as cylindrical, connecting portions to the stationary and movable members are formed at the upper and lower end portions and the side surface portion, and an elastic portion is formed at the middle portion.
 5. The sealing member as set forth in claim 4, which is formed of a material having flexibility.
 6. The sealing members as set forth in claim 4, wherein only the elastic portion is formed of a material having flexibility.
 7. The sealing member as set forth in any of claims 4-6, wherein the elastic portion is formed in an outwardly curved shape.
 8. The sealing members as set forth in any of claims 4-6, wherein the elastic portion is formed in an inwardly curved shape.
 9. The liquid pump as set forth in claims 1-3, wherein an annular sealing member is disposed between the upper-end margin of a fixing member for the stationary magnet and the end portion of a cylindrical attachment member disposed outside the rotary base member. 